Method for making a bump structure

ABSTRACT

Disclosed is a bump structure, which has a hollow body, for electrically connecting a first member and a second member. Also disclosed is a method for making a bump structure, which has the steps of: preparing a molding plate with a concave mold to mold a bump-forming member; forming a conductive thin film so as to form a predetermined cavity in the concave mold of the molding plate; preparing a substrate to which the conductive thin film is to be transferred; and transferring the conductive thin film formed on the molding plate to the substrate.

This application is a division of co-pending application Ser. No.09/188,203, U.S. Pat. No. 6,307,159 filed on Nov. 9, 1998, the entirecontents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to a bump structure, and more particularly to, abump structure for connecting mutually, e.g., electrodes or terminalsthat are formed and disposed on different electronic parts, and furtherrelates to a method for making such a bump structure.

BACKGROUND OF THE INVENTION

Conventionally, such a bump structure has been used to connect withelectrodes for IC inspection, for example, as disclosed in Japanesepatent application laid-open No. 8-50146 (1996). The bump structure ofJapanese patent application laid-open No. 8-50146 is, as shown in FIG.1, made by etching a substrate to form a cantilever, formingsingle-crystal silicon with a pointed shape on the cantilever byanisotropic-etching, forming metal film on the surface to form a probe.

Also, Japanese patent application laid-open No. 1-98238 (1989) disclosesa method for forming a connection structure with electrode by using atransfer technique. Namely, this known method is, as shown in FIG. 3,conducted by forming Ti film 5 and Pt film 6 on a bump structure formingsubstrate 4, coating resist film 7 thereon, forming Au bump structure 3on the substrate by plating. Then, after removing the resist film 7, asshown in FIG. 2, the Au bump structure 3 is transferred, while aligningthe Au bump structure 3 on the bump structure forming substrate 4, tothe Al electrodes 2 of a semiconductor element 1 by thermo-compressionbonding.

Further, Japanese patent application laid-open No. 7-167912 (1995)discloses an inspecting device using an anisotropic conductive film toelectrically connect with electrodes of IC etc. This inspecting deviceis provided with a bump structure, which is formed by making a hole inan organic resin film and filling the hole with metal, to be connectedwith the electrode or terminal of an inspected electronic piece.

However, there are several problems in the above conventionaltechniques. The first problem is that it is necessary to use a substratewith a specific structure to make the bump structure shown in Japanesepatent application laid-open No. 8-50146. Therefore, aconventionally-used substrate such as a printed-circuit board, which hasbeen generally in wide use, cannot be used. This is because it isnecessary to make concave portions at specific positions to get theflexibility of probe. Namely, in the printed-circuit board generallyused, such concave portions cannot be made. Thus, only a substrate ofsilicon can be used to make the bump structure shown in Japanese patentapplication laid-open No. 8-50146.

The second problem is that the height of bump structure has to bereduced when using the method for forming a bump structure shown inJapanese patent application laid-open No. 1-98238. This is because theresist becomes difficult to form when the pitch to form the bumpstructure is decreased. Namely, when decreasing the pitch to form thebump structure to increase the height, the resist film with a thicknesscorresponding to the height of the bump structure has to be formed andan aperture to decide the form of bump structure has to be formedthrough the resist film. However, the shape of the aperture is difficultto control as the thickness of the resist film increases.

Further, the third problem is that the bump structure cannot have such apointed tip that can be used as a probe contact when using the methodfor forming a bump structure shown in Japanese patent applicationlaid-open No. 1-98238. This is because the tip of the transferred bumpstructure in this method must be flat because the bump structure isformed on the planar substrate.

The fourth problem is that the bump structure may not be formed on anarbitrary electrode when using the method for forming a bump structureshown in Japanese patent application laid-open No. 8-50146. This isbecause it is difficult to form the mono-crystal silicon when theflatness of an electrode where the mono-crystal silicon is to be formedis not good. A further reason is that reagents such as alkali andhydrofluoric acid may damage the surface of substrate where the bumpstructure is to be formed when etching silicon or silicon dioxide film.

The fifth problem is that the method for forming a bump structure shownin Japanese patent application laid-open No. 8-50146 costs more. This isbecause the bump structure can be made only once from silicon forforming the bump structure.

The sixth problem is that it is difficult to make a probe to inspect ICor LSI with lattice-like electrodes by using the method for forming abump structure shown in Japanese patent application laid-open No.8-50146. That reason is as follows: The electrode interval of IC withthe lattice-like electrodes is about 250 μm. IC of 10 mm×10 mm haselectrodes of more than 1000, and IC of 15 mm×15 mm more than 3000. Whenextracting two-dimensionally this number of electrodes, it is necessaryto extract 50 wirings per 1 mm. This is equal to a wiring width pitch of20 μm. The wiring width pitch will be further reduced when consideringthat electrodes or etched concavity exists on the edge as well.Therefore, it becomes difficult to extract the wiring from a probe tothe outside.

The seventh problem is that the reliability of connection state isreduced when the bump structure, whose inside is filled with metal,shown in Japanese patent application laid-open No. 1-98238 is used toconnect substrates with different thermal expansion coefficients. Thisis because, when the bump structure is disposed between two substrateswith different thermal expansion coefficients to connect them, the bumpstructure does not transform because the entire bump structure is ofmetal. As a result, a large stress can be applied to the connectinginterface between the substrate and the bump structure, thereby causingthe separation or split.

The eighth problem is that the substrate for forming bump structure canbe repeatedly used only a few times in the method for forming a bumpstructure shown in Japanese patent application laid-open No. 1-98238.This is because there is no repairing method when the Pt film is injuredin the process of making the bump structure.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide a bumpstructure by which the electrical connection between electrodes orterminals of an electronic part such as IC and corresponding electrodesor terminals of a proper substrate or another electronic part can beefficiently, precisely and stably conducted.

It is a further object of the invention to provide a method for making abump structure where such a bump structure can be efficiently andinexpensively made.

According to the invention, a bump structure for electrically connectinga first member and a second member, comprises:

a hollow body.

According to another aspect of the invention, a method for making a bumpstructure, comprises the steps of:

preparing a molding plate with a concave mold to mold a bump-formingmember;

forming a conductive thin film so as to form a predetermined cavity inthe concave mold of the molding plate;

preparing a substrate to which the conductive thin film is to betransferred; and

transferring the conductive thin film formed on the molding plate to thesubstrate.

According to another aspect of the invention, a method for making a bumpstructure, comprises the steps of:

preparing at least two molding plates with a concave mold to mold abump-forming member;

forming a conductive thin film so as to form a predetermined cavity inthe concave mold of each of the molding plates;

bonding bump-forming members made of the conductive thin film formed oneach of the molding plates while keeping the outermost ends of thebump-forming members opposite to each other; and

separating the bump-forming member made of the conductive thin filmformed on one molding plate from the one molding plate, and transferringthe separated bump-forming member to the bump-forming member formed onanother molding plate.

According to another aspect of the invention, a method for making a bumpstructure, comprises the steps of:

preparing at least two molding plates with a concave mold to mold abump-forming member;

forming a conductive thin film so as to form a predetermined cavity inthe concave mold of each of the molding plates;

bonding bump-forming members made of the conductive thin film formed oneach of the molding plates while superposing the bump-forming members ina same direction; and

separating the bump-forming member made of the conductive thin filmformed on one molding plate from the one molding plate, and transferringthe separated bump-forming member to the bump-forming member formed onanother molding plate.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail in conjunction with theappended drawings, wherein:

FIG. 1 is a cross sectional view showing a conventional probe card,

FIG. 2 is a cross sectional view showing a conventional bump structure,

FIG. 3 is a cross sectional view showing a conventional bump structure,

FIGS. 4A and 4B are cross sectional views showing an example of a bumpstructure according to the invention,

FIG. 5 is a cross sectional view showing another example of a bumpstructure according to the invention,

FIG. 6 is a cross sectional view showing a way to use the bump structurein FIG. 5,

FIGS. 7A to 7E are illustrations showing the strain absorption effect ofa bump structure of the invention,

FIGS. 8A to 8E are cross sectional views showing an example of a methodof making a molding plate for forming bump-forming member used in theinvention,

FIG. 9A is a top view showing the details of an etch pit used in theinvention,

FIG. 9B is a cross sectional view showing the details of an etch pitused in the invention,

FIGS. 10A to 10F are cross sectional views showing an example of amethod of making a bump structure according to the invention,

FIGS. 11A and 11B are top views showing an etch pit and an aperture ofphotoresist according to the invention,

FIG. 12 is a top view showing the shape of plated film in a bump-formingmember according to the invention,

FIG. 13 is a cross sectional view showing a transfer operation in amethod of making a bump structure according to the invention,

FIG. 14 is a perspective view showing an example of notch shape in abump-forming member according to the invention,

FIG. 15A is a top view showing an etch pit and an aperture ofphotoresist to be made by a conventional method,

FIG. 15B is a cross sectional view showing an etch pit and an apertureof photoresist to be made by a conventional method,

FIGS. 16A and 16B are top views showing an aperture of etch pit used tomake another example of bump structure according to the invention,

FIGS. 17 to 23 are cross sectional views showing an example of a methodof making another bump structure according to the invention,

FIGS. 24 to 26 are cross sectional views showing an example of a methodof making a further bump structure according to the invention,

FIGS. 27 to 29 are cross sectional views showing an example of a methodof making a still further bump structure according to the invention,

FIG. 30 is a cross sectional view showing the connection of a bumpstructure in FIG. 29 to substrates

FIG. 31 is a cross sectional view showing an example of a method ofmaking a still yet further bump structure according to the invention,

FIG. 32 is a cross sectional view showing the connection of a bumpstructure in FIG. 31 to substrates

FIG. 33 is a cross sectional view showing an example of a method ofmaking another bump structure according to the invention,

FIG. 34 is a top view showing an etch pit and an aperture of photoresistaccording to the invention,

FIG. 35 is an illustration showing both a conventional bump structureand a bump structure of the invention used in the comparison experiment,

FIG. 36 is an illustration showing a substrate used in the comparisonexperiment,

FIG. 37 is a cross sectional view showing a method of making aconventional cylindrical bump,

FIGS. 38 and 39 are cross sectional views showing a method of making asample for reliability test, and

FIG. 40 illustrates an embodiment of the present invention including atwo-layered structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A bump structure and a method for making a bump structure in thepreferred embodiment according to the invention will be explained below,referring to the drawings.

FIGS. 4A and 4B are cross sectional views showing the composition of anexample of a bump structure 1 of the invention. In FIGS. 4A and 4B, thebump structure 1, which electrically connects a first member 2 and asecond member 3, is composed of a cavity 4.

The bump structure 1 of the invention is preferably provided with atleast one point-contact part 5.

Also, a bump-structure-forming member(hereinafter referred to as‘bump-forming member’), which composes the bump structure 1 of theinvention, has the shape of a multangular pyramid including aquadrangular pyramid and a triangular pyramid, a cone or a hemisphereetc. Also, as shown in FIG. 5, it has a shape formed as a combination ofat least two bump-forming members 11, 12 which have any of the aboveshape.

Namely, this example of the bump structure 1 of the invention and theother examples can be, as shown in FIG. 5, formed by bonding at leasttwo bump-forming members so that to provide a cavity inside.

In these examples, the two mutually-bonded bump-forming members 11, 12may be a same shape or different shapes to each other.

By reason that the bump structure 1 of the invention is composed asabove-mentioned, the bump-forming member 11 may be, for example as shownin FIG. 4A, bonded directly to a proper substrate or through a properbonding means to a predetermined electrode 6 of the electronic element2. Alternatively, as shown in FIG. 5, the hollow bump structure 1 thatthe two bump-forming members 11, 12 are bonded mutually may be bondeddirectly to a proper substrate or through a proper bonding means to thepredetermined electrode 6 of the electronic element 2.

Taking the case of FIG. 5, one protrusion 5′ of the bump structure 1 isconnected through a solder 113 to an electrode 112 disposed on a propersubstrate 2.

FIG. 6 shows the case that the bump structure 1 in FIG. 5 is connectedto another electronic element or substrate 3. Another protrusion 5 inFIG. 5 is connected through a solder 113 to an electrode 112 disposed onthe substrate 3.

The bump structure 1 of the invention shown in FIGS. 5 and 6 can betransformed from the original shape, for example, when an externalstress is applied in the direction of arrows a and b in FIGS. 7A and 7Bor arrows c and d in FIGS. 7C and 7D. Therefore, it can absorb theexternal stress to stabilize the connection structure.

Similarly, the bump structure 1 can absorb a distortion even when athermal stress is applied to the electronic element or substrate, oreven when, at heating atmosphere, the dimensions of the electronicelements or substrates become different from each other due to thedifference between the thermal-expansion coefficients of the electronicelements or substrates to be used.

Also, as shown in FIG. 7E, the bump structure 1 shown in FIGS. 4A and 4Bcan get the same effect as mentioned above by forming an opening 8 witha proper size at part of the bump structure 1 to make its own frame ofthe bump structure 1 flexible.

Such a flexible frame of bump structure can be, of course, applied tothe other example of the invention in FIG. 5.

The bump structure 1 of the invention can be provided by making thebump-forming member 11 by forming a predetermined conductive film on afor forming bump-forming member, which is a proper substrate providedwith a molding part to form the bump-forming member 11 to compose thebump structure 1, transferring it to a predetermined position of aproper substrate or a predetermined electronic element.

Therefore, a bump-forming member to form the bump structure can beprovided with an arbitrary shape by properly designing the molding partdisposed on the molding plate for forming the bump-forming member.

Moreover, in the invention, the molding part can be, as described later,easily formed and arbitrarily designed as to its size, height, shape,formation density etc.

Namely, the bump structure 1 of the invention is characterized by thatit is composed transferred film formed by using a predetermined mold.

Further, in this invention, the bump structure 1 is desirably formed byat least one conductive film with a bent form, and is desirably composedby at least two films laminated.

In further detail, the at least two films to form the bump structure 1are desirably composed of materials with characteristics different fromeach other. Specifically, it is desirable that, of the at least twofilms, a first film 601 to form the surface that directly contacts theelectrode or terminal of a substrate to which the bump structure 1 facesis of rhodium or platinum and a second film 602 bonded to the first filmis of nickel, as illustrated in FIG. 40.

A method for making the bump structure 1 in the invention will beexplained below. Basically, it uses sputtering, etching,photolithography etc. Thereby, the design and fabrication of the bumpstructure 1 above-mentioned can be easily and efficiently conducted.

An example of the method for making the bump structure 1 in theinvention will be explained, referring to FIGS. 8A to 11B.

First, as a first step to make the bump structure 1 of the invention, amolding plate will be made provided with such a predetermined moldingpart that the bump-forming members 11 or 12 to form the bump structure 1can preferably have its tip portion with a pointed or point contact.

Namely, FIGS. 8A to 8E show an example of a method of making a moldingplate 10 for forming the bump-forming member by using a silicon wafer tomold, for example, the bump structure 1 with the shape shown in FIGS. 4Aand 4B.

This example is shown for the case that the molding plate 10 is made sothat the bump-forming member 11 to form the bump structure 1 in FIGS. 4Aand 4B has a quadrangular pyramid form. The shape, arrangement interval,size and arrangement form of the molding part 104 can be, as describedearlier, suitably changed according to the arrangement state ofelectrodes or terminals of electronic element desired to form theconnection structure.

Also, FIGS. 8A to 8E show the method for making the molding plate 10 forforming the bump structure.

As shown in FIG. 8A, a (100)-crystal-orientation silicon wafer substrate100 with a diameter of 6 inches and a thickness of 1 mm is prepared, andthermal oxidation films 101 of 1 μm thick are formed on both surfaces ofthis wafer.

Then, as shown in FIG. 8B, photoresist 102 of 5 μm thick is coated. Thisis exposed using a predetermined mask and developed to form an aperture103 in the photoresist 102.

The aperture 103 is opened corresponding to a position of IC electrodeto which a point-contact terminal is transferred. The sides of theaperture 103 are parallel or perpendicular to <100>.

As shown in FIG. 8C, the silicon wafer 100 is treated with bufferedhydrofluoric acid to remove the thermal oxidation film under theaperture 103 in the photoresist 102, and then the photoresist 102 isremoved by solvent.

Then, as shown in FIG. 8D, the silicon wafer 100 is anisotropic-etchedwith 10% potassium hydroxide solution to make a concavity (etch pit) 104with (111) plane.

The details of part f in FIG. 8D are shown in FIGS. 9A and 9B. As shownin FIGS. 9A and 9B, in the after-etching stage, the thermal oxidationfilm 101 is formed protruding into the etch pit 104 and such part causeshooking in the later transfer process. Therefore, as shown in FIG. 8E,the thermal oxidation film 101 over the etch pit 104 is thoroughlyremoved by treating with buffered hydrofluoric acid.

The thermal oxidation film 101 is left on the back face of the substrate100 to insulate it. Because of this, the back face does not need to bemasked in the later plating process.

By the above processes, the molding plate 10 for forming thebump-forming member is made.

Next, a method for making the bump-forming member 11 or 12 by using themolding plate 10 for forming the bump-forming member will be explained,referring to FIGS. 10A to 10F.

As shown in FIG. 10A, 1 μm sputtered film 105 of copper is formed on themolding plate 10 for forming the bump-forming member. Then, as shown inFIG. 10B, photoresist 102 of 15 μm thick is coated, and then an aperture103 is formed by exposing the photoresist 102 with a predeterminedpattern.

In this process, as shown in FIG. 11A, edge part 32 of the aperture 103is controlled to be, e.g., 5 μm smaller than a corner 31 of the etch pit104 in the molding plate 10 for forming the bump-forming member.

Then, by laminating films of, e.g., 1 μm rhodium, 10 μm nickel and 5 μmgold thereon in this order by electrolytic plating, plated film 106 tocompose the bump-forming member 11 is formed.

In this invention, it is advantageous for the separation and transferprocesses, described later, of the invention that the first layer tocontact directly the electrode or terminal of an inspected electronicelement uses rhodium with a high film stress as well as a conductivity.However, platinum can be also used, as the case may be.

FIG. 10C is a cross sectional view cut along the dotted line in FIG.11A, and FIG. 10D is a cross sectional view cut along the dotted line inFIG. 11B.

Namely, in this invention, in forming the plated film 106, photoresist102 is left on at least one corner 31 of the etch pit 104 so as not toform the plated metal film above-mentioned on that part. This structureallows the plated metal film 106 to be easily released from the siliconmold 104.

As shown in FIGS. 10E and 10F, after removing the photoresist 102, it issoaked in a solution of 5% sulfuric acid and 5% hydrogen peroxide for 20seconds to etch the copper sputtered film 105 by 0.5 μm, then washed bypure water.

FIG. 10F is a cross sectional view showing the state after etching thesputtered film 105 in FIG. 10E.

As shown in FIG. 12, the copper sputtered film 105 is partially etchedto make exposed part 108 where the underlying silicon wafer 100 isexposed. In this case, etching of the exposed part 108 can be easilyconducted because the corner 31 is not covered with the plated film 106.Also, the etching rate at the boundary of the etch pit and the siliconwafer surface is higher than that at the plane because the boundary isshaped convex.

In this process, metal of the plated film 106 to form the tip portion 5of the bump structure 1 of the invention can also dissolve when it is ofsome material, e.g., nickel. However, it makes no problem because theamount of dissolution is up to about 2 μm.

By thus processing, in the later process, the plated film 106 can beeasily released from the etch pit 104 of the molding plate 10 forforming the bump-forming member when the bump-forming member 11 istransferred to a proper electronic element or substrate.

Also, in this invention, the thermal oxidation film 101 on the siliconsubstrate 100 is removed, and the film can be therefore easily releasedwithout being hooked by any structural part.

Next, an example of a method of transferring the bump-forming member 11formed on the molding plate 10 for forming the bump-forming member to aproper substrate 2 will be explained.

Namely, as shown in FIG. 13, the bump-forming member 11 described aboveis formed on the molding plate 10 for forming the bump-forming member.

Though in this invention a plurality of the bump-forming members 11 are,of course, formed on the molding plate 10 for forming the bump-formingmember with a predetermined arrangement density and a predeterminedarrangement form, the following explanations will be given provided thatone bump-forming member 11 is, convenience of explanation, formed.

For example, on the molding plate 10 for forming the bump-formingmember, the etch pits 104 are disposed at intervals of 250 μm. Namely,similar patterns exist within 10 mm×10 mm and the total number of theetch pits 104 is 1600.

As shown in FIG. 13, for example, a substrate 2 where a proper electrode112 is formed on its principal plane S1 is prepared additionally.

For example, the substrate 2 may be composed so that the electrode 112is electrically connected through a conductive member 16 filled in a viahole 15 penetrating the substrate 2 to a wiring 14 formed on anotherprincipal plane S2.

Then, the substrate 2 and the bump-forming member 11 formed on themolding plate 10 for forming the bump-forming member are mutuallyjointed while aligning by using a proper device, for example, both arejointed and fixed by heating and pressing.

Then, when the release operation is conducted by moving the moldingplate 10 for forming the bump-forming member and the substrate 2 in thedirections that both are distanced from each other, the bump-formingmember 11 composed of the plated film 106 can be transferred to thesubstrate 2, thereby obtaining the bump structure 1 shown in FIGS. 4Aand 4B.

In FIG. 13, when the plated film 106 and the electrode 112 are composedof aluminum, by heating at 350° C. and pressing at 20 g after thealigning, the plated film 106 can have been transferred to the electrode112.

The bump structure 1 of the invention is, as apparent from the aboveexplanations, fixed to a predetermined principal plane of at least onebody.

In this invention, notched part 50 shown in FIG. 14 is formed by, asdescribed above, disposing photoresist on at least a part of the corner31 of the etch pit 104, the molding part formed on the molding plate 10for forming the bump-forming member, so as not to form the plated film106 on that part. Therefore, when applying a releasing stress aftercompression-bonding the bump-forming member 11 to the electrode 112, theconcentration of stress occurs at that part to promote the releasing atthe interface of the plated film 106 and the silicon wafer.

Also, by removing the copper film by etching as shown in FIG. 10F, thereleasing of the plated film 106 from the silicon wafer can be furtherpromoted.

Therefore, the occurrence of non-transfer failure can be suppressed whenthe point-contact terminal is transferred.

After the transferring, the surface of the bump-forming member 11including copper sputtered film 105 and the etch pit 104 of the moldingplate 10 for forming the bump-forming member is etched by a solution of5% sulfuric acid and 5% hydrogen peroxide for 60 seconds, then washed toremove them.

As a comparative example, different from the structure of the invention,a probe with a point contact terminal formed by the conventional method,where the plated film 106 is continuously formed around the etch pit 104as shown in FIGS. 15A and 15B, is formed. The releasing effect in thetransfer operation is compared and considered.

For the bump-forming member 11 by the conventional method, even whenetching the copper sputtered film 105, the corner 31 can be etched onlyfrom its edge because it is covered with the plated film 106 as shown bypart c in FIG. 15B.

Therefore, the etch process is delayed, and it can be etched about 10 μmwhen the sputtered film 105 for a long time is etched. The etch depthdepends on a dispersion in the etch condition, pattern precision,thickness of plated film and film stress.

Namely, in the conventional method, the etch rate is dispersed dependingon the bump-forming member 11. Therefore, for the high etch rate, themost part of copper has to be etched and the bump-forming member 11 hasto be released from the casting mold 10 when being washed before thetransferring.

Also, there occurs the problem that nickel etc. in the plated film 106to form the bump-forming member 11 can dissolve by 10 μm to 20 μm.

Next, the release and transfer test of the bump-forming member 11 wasconducted using the bump-forming member 11 obtained by the method ofthis invention and the bump-forming member 11 formed by the conventionalmethod mentioned above.

The bump-forming members 11 used in this test are arranged square on asix-inch wafer, and the total number of point-contact terminals is32000.

The results of the case that they are transferred to the aluminumelectrodes of an IC-formed wafer at 20 g per point-contact terminalwhile heating at 350° C. for 10 seconds are as follows:

bump-forming member: number of good transferred products/total numberbump-forming member with notched corner 100/100 bump-forming memberwithout notched corner  5/100

Namely, in the bump-forming member 11 without the notched corner 31, thetransfer ratio cannot be enhanced because the releasing of thebump-forming member 11 is not promoted. In the case that the etch timefor copper before the transferring is lengthened to enhance the transferratio in case of no notched corner 31, the number of bump-formingmembers dropping before the transferring and the number of transferredbump-forming members are as follows:

The cause of transfer failure in bump-forming member without notchedcorner (number of ICs)

The cause of transfer failure in bump-forming member without notchedcorner (number of ICs) number of good number of number of members leftetch time (sec) transfer dropping on bump-forming mold  10 5  0 95 100 338 59 200 0 98  2

Judging from the above experimental results, the transfer ratio is lowbecause the bond strength between the wafer and the plated film when theetch time of the sputtered film 105 is short. The plated film 106 isreleased from the substrate in the process of before the transferringwhen the etch time is long.

The Silicon wafer used in forming the bump-forming member is reusedafter dissolving all copper by soaking it in an etch solution ofsulfuric acid and hydrogen peroxide.

Pollution etc. adhered in the process can be released by dissolvingcopper. Thus, even when using it many times, there does not occur theproblem that pollution is adhered.

In contrast with this invention, in case of the structure in Japanesepatent application laid-open No. 1-98238, the mold must be discardedbecause there is no method for releasing Pt film when the Pt film isinjured.

Further, the following comparison experiment is conducted so as to checkout the difference on effect between the bump structure with hollow bodyof the invention and the conventional cylindrical and solid-core typebump structure.

Namely, for the bump structure of the invention and the convention bumpstructure, the comparison experiment as to the absorption of dispersionin the height of an electrode to be bonded with them is conducted.

Test Method:

A test to connect an IC chip that aluminum electrodes are formed on asilicon wafer of 10 mm×10 mm, 470 μm thick with a glass ceramicsubstrate is conducted.

320 chip electrodes are disposed at pitches of 120 μm around the chip.As the bump to connect this chip to the glass ceramic substrate, theconventional cylindrical (the entire core is filled with plating metal)bump shown in FIG. 35A and the hollow bump of the invention shown inFIG. 35B are used.

On the aluminum electrode of the chip, 1 μm thick electroless zincplated film, 1 μm thick electroless nickel plated film and 1 μm thickelectroless gold plated film are formed.

As shown in FIG. 36, the glass ceramic substrate 300 used herein is amultilayer wiring substrate, and the surface of the substrate is somounded by about 5 μm over about 100 μm wide as to provide convex parts301 due to inner-layer wirings 302.

On this substrate 300, there are electrodes formed corresponding to thechip electrodes. Most of the electrodes are formed on even places on thesubstrate, but about 10 electrodes are formed on the convex parts.

An example of the process of forming the bumps on the chip is shown inFIG. 37.

The cylindrical bump has a diameter of 60 μm and a height of 30 μm. Thisbump is made as described below.

As shown in FIG. 37, on the glass substrate, chrome-sputtered film,palladium-sputtered film 320 and ITO conductive film 330 are formed.Then, plating resist 340 is coated thereon to form a pattern ofapertures 350 of 60 μm wide and 30 μm thick.

On the glass substrate 310, 2 μm gold plated film, 2 μm nickel platedfilm and 2 μm gold plated film are formed by electrolytic plating.

The bump of the invention is of 70 μm bottom and 50 μm high. Thecomposition of material is 5 μm gold, 10 μm nickel and 1 μm rhodium,from the inside of the bump plated film.

This is aligned to the chip electrode, pressed at a load of 50 g perbump while heating the transfer substrate at 350° C., transferred to thechip electrode.

These bump-formed chips are pressed aligning to the electrode of theglass electrode. In the conventional bump, even when the pressure topress the chip is increased to 20 kg, there are some electrodesunconnected.

The unconnected electrodes are for two to three bumps adjacent to theconvex part shown.

When the chip using the bump of the invention is similarly pressed, allthe electrodes can be connected at a pressure of 500 g.

This is because the bump of the invention is easy to transform as it isformed with 16 μm thick plated film and it is hollow and because it isfurther easy to transform as the plated film of the bump is partiallynotched around the connection part of the chip and the bump.

Also, it is because the connection part is not opened even when thedistance between the chip and the substrate varies about 3 μm, as mostof the transforming of plated film is composed of elastic transform.

Reliability Test Results:

In the same way as described above, the conventional cylindrical bumpand the bump of the invention are transferred to a chip 410. This is, asshown in FIGS. 38 and 39, connected to electrodes on an aluminasubstrate 400, then sampled for the reliability test.

The connection is made as shown. The procedures are as follows:

Epoxy resin 420 including 70 wt % silica filler is dropped at the centerposition of the alumina substrate 400 to mount the chip 410, and thenthe chip 410 bump-formed is aligned and pressed against here.

A load to press is 20 kg for the cylindrical bump and 1 kg for the bumpof the invention. By heating at 200° C. for 1 min. in this state, epoxyresin is hardened and sampled for the reliability test.

In this sample, the bump formed on the chip and the electrode of thesubstrate are kept pressed to each other by the hardened resin.

Reliability test conditions:

A heat cycle test where a retention at −40° C. for 30 min. and aretention at 120° C. for 30 min. compose one cycle is conducted.Measuring the resistivity of connection part, a failure is determinedwhen the resistivity increases higher than 20%. For each sample, 10chips are tested.

test result (number of good chips) number of cycles 100 200 400 600 1000conventional  10  10  8  3   0 present invention  10  10  10  10  10

In the bump of the present invention, the connection failure does notoccur until 1000 cycles.

In the heat cycle, a shear stress is applied among the chip, epoxy resinand alumina substrate because their thermal expansion coefficients aredifferent from each other. The thermal expansion coefficients are asfollows:

chip: 3 ppm

epoxy resin: 30 ppm

alumina substrate: 10 ppm

Due to such differences on thermal expansion coefficient, a stress isapplied repeatedly. In this case, when using the conventionalcylindrical bump for the connection part, the connection part must beopened when the distance between the chip and the alumina substrate iswidened by that epoxy rein is transformed only a bit (for example, 2 μm)by repeated stress, because it has little elasticity.

The bump of this invention is elastic-transforming by about 5 μm whilebeing pressed by a load of 1 kg to be applied when making the sample.even when epoxy resin is similarly transformed, the connection part isnot opened because it can transform by the restoring force based on thebump's elasticity. Therefore, it presents excellent connectionreliability.

Next, an example of a method of making the bump structure 1 of theinvention composed as shown in FIG. 5 will be explained.

Namely, in this example, using the steps up to FIG. 10F, twobump-forming members 11, 12 with a same structure or slightly differentstructures are made by using separate molding plates 10, 10′ for formingthe bump-forming member.

For example, like the example in FIGS. 10A to 10F, by forming an etchpit 104 with a predetermined shape on a six-inch silicon wafer, the twomolding plates 10, 10′ for forming the bump-forming member are made. Byconducting the same operations as in FIGS. 10A to 10F, copper sputteredfilm 105 and photoresist 102 are formed.

In this example, photoresist to cover the corner 31 of the etch pit 104is preferably of patterns different from each other as shown in FIGS.16A and 16B, while it may be of the same pattern.

This is advantageous when conducting separately the transfer operationof the bump-forming member 11, described later, from the two moldingplates 10, 10′ for forming the bump-forming member 11.

For example, as shown in FIGS. 16A and 16B, they have different patternsof photoresist 102, where parts to cover the corner of the etch pit 104in photoresist 102 have different sizes.

Namely, one molding plate 10′ for forming the bump-forming member hasthe pattern shown in FIG. 16A, where photoresist 102 covers 15 μm fromthe corner 31 of the etch pit 104. The other molding plate 10 forforming the bump-forming member has the pattern shown in FIG. 16B, wherephotoresist 102 covers 5 μm from the corner 31 of the etch pit 104.

On each of the two molding plates 10, 10′ for forming the bump-formingmember, like the first example described earlier, 1 μm rhodium, 10 μmnickel and 5 μm gold are laminated, thereby plated film 106 is formed.Then, the bump-forming substrates 10, 10′ are soaked in a solution ofsulfuric acid and hydrogen peroxide for 20 seconds to slightly etch thecopper sputtered film 105, then washed.

The two bump-forming members 11, 12 thus formed are, as shown in FIG.17, aligned, bonded and fixed together while heating at 350° C. andpressing at 50 g per bump.

Namely, in the second example of the invention, the two bump-formingmembers 11, 12 made via separate processes as described above are bondedwhile their opened ends, i.e., the outermost ends of the bump-formingmembers 11, 12, are faced to each other, so that a cavity is formedinside.

Further, this invention is characterized by that there is formed atleast one notched part 50 near the outermost ends of the twobump-forming members 11, 12 mutually bonded.

Such notched part 50, as described earlier, has the effect that itallows the plated film to be easily released from the substrate whenseparating the bump-forming members 11, 12 from the molding plates 10,10′ for forming the bump-forming member so as to transfer them.

Further, in this invention, it is desirable that the notched parts 50formed near the outermost ends of the two bump-forming members 11, 12mutually bonded have shapes different from each other.

Namely, in this example of the invention, by separating the bump-formingmembers 11, 12 from the molding plates 10, 10′ for forming thebump-forming member in the transfer operation described above, the bumpstructure 1 with pointed ends is formed.

Also, when separating the molding plate 10′ for forming the bump-formingmember, as shown in FIG. 18, the plated film 106 on the molding plate10′ for forming the bump-forming member can be released easier than onthe molding plate 10 for forming the bump-forming member, because thepatterns of the plated film 106 are different between the twobump-forming members 11, 12, as described above.

Further, for example, by etching only the copper sputtered film 105 ofthe molding plate 10′ for forming the bump-forming member, only theplated film 106 of the bump-forming member 11 with the pattern in FIG.16A is released as shown in FIG. 18.

Then, the bump-forming member 12 with the pattern in FIG. 16B to whichthe bump-forming member 11 is transferred is soaked in a solution of 5%sulfuric acid and 5% hydrogen peroxide for 20 seconds to partially etchthe copper sputtered film 105, then washed.

This is pressed against a substrate coated with flux of 20 μm, therebythe flux 110 is transferred as shown in FIG. 19.

Then, as shown in FIG. 20, it is soldered to the copper electrode 112′,on which solder 113′ is coated, of, e.g., an IC-formed electronic partor proper substrate 2 while heating at 250° C. After cooling, byseparating the molding plate 10 for forming the bump-forming member, thebump structure 1 as shown in FIG. 5 is obtained.

Cutting the substrate composed of IC wafer 2 etc. where the bumpstructure 1 is thus formed, a predetermined electronic part, e.g., an ICchip, is obtained.

In conducting the electrical test of a bare chip, IC 2 with the bumpstructure 1 composed according to the invention can be electricallyconnected if only it is aligned and pressed to the electrodes of aninspecting wiring board, because the bumps 1 on IC 2 are pointed anduniform in height and because the center part of bump is elastic.

Therefore, a conventionally-used probe card is not necessary and a barechip tested can be obtained at a low cost.

Also, in this invention, as shown in FIG. 6, IC 2 with the bumpstructure 1 is aligned and bonded to the electrode 112 of the wiringboard 3 with solder 113 while heating at 250° C. It can be easilymounted because the electrode pitch is as narrow as 60 μm and the bumpheight is 60 μm.

In the bump structure 1 of the invention, even when strain is applied tothe connection part due to a thermal-expansion difference between IC andthe material of wiring board as the surrounding temperature varies afterconnecting with the electrode of an electronic part such as IC or awiring board, the shearing transform strain can be absorbed because thebump film can transform around the center of the bump structure 1 asshown in FIGS. 7A and 7B. Therefore, the reliability of connection partcan be obtained even when the thermal-expansion difference between ICand the wiring board exists.

Next, a third example of the bump structure 1 according to the inventionwill be explained.

In this example, a bump structure with a high aspect ratio is made.Especially the process of connecting IC2 to the aluminum electrode 112will be explained below.

Like the second example of the invention, by heating and pressing thetwo molding plates 10, 10′ for forming the bump-forming member, the bumpis transferred from one wafer 3 to another. As shown in FIG. 21, resist102 is coated on the wafer 3 on which the bump-forming member 11 isformed, the bump 11 is exposed by patterning, electrolytic gold plating114 of 10 μm is formed thereon.

This is aligned to the aluminum electrode 112 of IC 2, then the bump istransferred while heating at 350° C. and pressing at 20 g per bump. Thecross sectional form after the transferring is shown in FIG. 22.

In this example, the bump structure with an aspect ratio larger than theabove-mentioned examples can be formed. Also, the connection part of IC2 to the electrode 112 is located at the center of the electrode.Therefore, it can be connected to a smaller electrode.

A fourth example of the bump structure 1 according to the invention willbe explained below.

In this example, like the first example, the molding plate 10 forforming the bump-forming member is made, the copper sputtered film isformed thereon, photoresist is coated. After plating 1 μm rhodium and 10μm nickel thereon, 5 μm tin-zinc eutectic solder, in place of goldplating in the first example, is plated.

This plated film is formed into the bump by melting the copper electrodeof IC and the solder. This example is suitable for the case that thebump structure is formed on area-bump IC etc. where electrodes areformed at the entire device-forming region unbearable to temperature andpressure to be thermally-compressed with gold.

A fifth example of the bump structure 1 according to the invention willbe explained below.

In this example, the bump structure 1 is characterized in that it iscomposed of at least two bump structures, which are superposed in thesame direction, with a same structure or different structures.

Specifically, as shown in FIG. 24, like the first example, the platedfilm 106 is transferred onto the electrode 112, thereby the bumpstructure 1 is formed as shown in FIG. 25.

Next, like the fourth example, using the other molding plate 10′ forforming the bump-forming member, plated film 106′ of rhodium, nickel andsolder plating is formed. Then, as shown in FIG. 26, the bump structure1 in FIG. 25 is overlapped and bonded to the plated film 106′ whileheating at 250° C.

By thus overlapping the bump structure, the aspect ratio of bump can beincreased.

Thus, in this example, the bump structure 1 of 40 μm wide and 60 μm highis obtained at 60 μm pitch.

A sixth example of the bump structure 1 according to the invention willbe explained below.

In this example, as shown in FIG. 27, like the second example, twobump-forming members 11, 12 are formed by using two molding plates 10,10′ for forming the bump-forming member, and then the bump-formingmember 11 on one molding plate 10 for forming the bump-forming member istransferred to the bump-forming member 12 on the other molding plate 10′for forming the bump-forming member.

As shown in FIG. 28, varnish 109 of, e.g., photosensitive polyimide iscoated on the surface of the bump-forming mold 10 where the bump-formingmember 12 is left, patterned so that the tip of the bump-forming member11 is exposed, hardened at 300° C. to make film.

As shown in FIG. 29, this is soaked in a solution of 10% sulfuric acidand 10% hydrogen peroxide to dissolve the copper sputtered film 105,thereby anisotropic conductive film 110 with pointed ends on both sidesis formed.

The bump structure 1 of this example has a high ability to contactpenetrating through the surface of electrode to be connected even if itis oxidized, because the both ends are pointed.

In the example disclosed in Japanese patent application laid-open No.7-167912, connection failure occurs when some pollution such as oxidefilm and organic film exists on an electrode to be connected, becauseits tip part is rounded.

Namely, in this example, by burying at least a part of the bumpstructure 1 with a predetermined synthetic resin material etc., theanisotropic conductive film where the bump structure 1 is fixed on theplane is obtained.

To compare the effect of the bump structure 1 of the invention with thatof the conventional example, a simulative experiment is conducted usinga wiring board polluted by 0.5 μm resist thin film.

With a sample in Japanese patent application laid-open No. 7-167912, theelectrical connection was not obtained even when pressing at 20 g perbump. However, with a sample in this example, the electrical connectionis obtained if only pressing 0.5 g per bump. Thus, the bump structure 1of the invention has a high ability to penetrate through the pollutionbecause the tip part is pointed.

FIG. 30 shows the case that the anisotropic conductive film 110 of theinvention is sandwiched by two wiring boards 2, 3 and pressed at 100 gper bump structure. Thus, even if the an excessive pressure is appliedafter contacting, it does not apply an excessive stress to theelectrodes 112, 112′ of the wiring boards 2, 3 because the plated film106 is deformed as shown in FIG. 30.

A seventh example of the bump structure 1 according to the inventionwill be explained below.

In this example, like the sixth example, anisotropic conductive film isformed as shown in FIG. 31, but cardo resin 116 is used in place ofpolyimide.

The cardo resin 116 is bonded to wiring boards 2, 3 while heating at350° C. and pressing at 5 kg/cm². As shown in FIG. 32, the two wiringboards 2, 3 are aligned, heated and pressed sandwiching the anisotropicconductive film 110 therebetween to get the electrical and mechanicalconnection.

An eighth example of the bump structure 1 according to the inventionwill be explained below.

In this example, the bump structure 1 is made like the first example. Asshown in FIG. 33, polyimide pattern 109 is formed on the molding plate10 for forming the bump-forming member, then patterning and plating inlike manner, the height of bump is thereby increased by 10 μm.

Namely, in this example, by adjusting the film thickness of polyimide109, the aspect ratio of bump structure can be controlled.

An ninth example of the bump structure 1 according to the invention willbe explained below.

In this example, when copper sputtered film and photoresist are formedon the molding plate 10 for forming the bump-forming member like thefirst example, an aperture 103 is formed by a pattern in FIG. 34.

Thus, in this example, a relatively large opening is formed on the sidesof the bump-forming member.

Namely, in forming the plated film 106, resist is, in advance, disposedas shown so as not to form plated film 106 at that part. On the sides ofthe bump-forming member, the relatively large opening can be formed asshown in FIG. 7E. As a result, the bump structure 1 that is sostructured as shown in FIGS. 4A and 4B can also have a reduced strength,thereby bringing out a flexible characteristic to pressing or lateralbiasing. Therefore, the absorption of strain or the absorption ofpressing external force and further the connection between unconformableelectrodes can be enhanced.

Namely, when the bump structure 1 in this example is pressed against ICelectrode, the concentration of stress is difficult to happen, comparedwith the first example. Even when IC is pressed against a substrate atan excessive pressure, electrodes on IC or substrate are not broken.

Advantages of the Invention

In the bump structure of the invention as composed above, the firstadvantage is that bumps used to connect IC and wiring board can be madeinexpensively. This is because bumps formed by plated film aretransferred and are in one lump mass-produced.

The second advantage is that transferring of bumps used to connect ICand wiring board can be conducted at a high yield ratio. This is becausethe release from bump-forming mold can be promoted by providing a notchwhen plated film is formed.

The third advantage is that bumps with uniform height and pointed tipcan be produced at a narrow pitch. This is because plated film formed byusing fine-processed etch pit is transferred.

The fourth advantage is that bumps with high aspect ratio can beproduced at a narrow pitch. This is because the height of bump can bedoubled by bonding two bumps formed by using separate substrates. Also,alternatively, another bump can be overlapped to a transferred bump.

The fifth advantage is that bumps with flexibility can be produced. Thisis because it has a hollow structure formed by bonding bumps and it cantransform by notches formed at its center part.

Further, the number, density and shape of bump structure 1 formed on asubstrate can be arbitrarily adjusted to match the arrangement state orpattern of electrodes or terminals on an electronic part to be connectedtherewith.

Also, in this invention, the bump-forming member is made, for example,by forming sputtered film on the etch pit of silicon substrate,patterning resist thereon, plating. In this process, part of resistpattern is formed to cover, e.g., the corner of the etch pit and theaperture of resist is controlled to be smaller than the etch pit whenplating is conducted. Thus, after removing the resist and etching thesputtered film, the bump-forming member can be easily transferred toanother substrate by thermal compressive bonding or soldering.

Namely, in this invention, a precise and point-contact terminal withpointed tip can be formed by using the silicon etch pit as a mold.Further, by sputtering copper on the silicon, the bump-forming member 10can be easily released in the later process.

Also, in this invention, the photoresist pattern for forming plated filmto compose the bump-forming member 10 is so made that the photoresist102 also covers the corner 31 of the etch pit 104, as shown in FIGS. 11Aand 11B. Therefore, when the point-contact terminal 10 is transferred inthe later process, it can be easily released by etching copper.

Further, in this invention, when transferring the point-contactterminal, it is separated with the sputtered film. Also, the sputteredfilm left on the molding plate for forming bump-forming member isdissolved. Thereby, the sputtered film can be removed. Therefore, evenwhen the mold is used repeatedly, pollution or injure does not occur informing the bump-forming member.

Further, in this invention, the point-contact terminal can be madeinexpensively because the silicon wafer with etch pit 104 can be usedrepeatedly.

Although the invention has been described with respect to specificembodiment for complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodification and alternative constructions that may be occurred to oneskilled in the art which fairly fall within the basic teaching here isset forth.

What is claimed is:
 1. A method for making a bump structure, comprisingthe steps of: preparing at least two molding plates with a concave moldto mold a bump-forming member; forming a conductive thin film so as toform a predetermined cavity in the concave mold of each of the moldingplates; bonding bump-forming members made of said conductive thin filmformed on each of the molding plates while keeping the outermost ends ofsaid bump-forming members opposite to each other; and separating saidbump-forming member made of said conductive thin film formed on onemolding plate from said one molding plate, and transferring saidseparated bump-forming member to the bump-forming member formed onanother molding plate.
 2. A method for making a bump structure,according to claim 1, further comprising the steps of: connecting saidbump-forming member formed on said another molding plate to apredetermined electrode on a substrate prepared; and separating saidbump-forming member formed on said another molding plate from saidanother molding plate.
 3. A method for making a bump structure,according to claim 2, wherein: said at least two bump-forming members tobe bonded mutually are provided with at least one notch near theoutermost end of each of said members.
 4. A method for making a bumpstructure, according to claim 3, wherein: said at least one notch isprovided with different shapes between said bump-forming members.
 5. Amethod for making a bump structure, according to claim 1, wherein: saidat least two bump-forming members to be bonded mutually are providedwith at least one notch near the outermost end of each of said members.6. A method for making a bump structure, according to claim 5, wherein:said at least one notch is provided with different shapes between saidbump-forming members.
 7. A method for making a bump structure,comprising the steps of: preparing at least two molding plates with aconcave mold to mold a bump-forming member; forming a conductive thinfilm so as to form a predetermined cavity in the concave mold of each ofthe molding plates; bonding bump-forming members made of said conductivethin film formed on each of the molding plates while superposing saidbump-forming members in a same direction; and separating saidbump-forming member made of said conductive thin film formed on onemolding plate from said one molding plate, and transferring saidseparated bump-forming member to the bump-forming member formed onanother molding plate.
 8. A method for making a bump structure,according to claim 7, further comprising the steps of: covering at leastone part of a plurality of said bump-forming members formed on saidanother molding plate with an insulating material; and separating saidplurality of said bump-forming members from said another molding plate.9. A method for making a bump structure, comprising the steps of:providing a molding plate having a concave mold for a hollow bumpstructure; forming a photoresist layer on the molding plate; depositinga conductive film in the concave mold and above a peripheral portion ofthe photoresist layer around the concave mold so that the conductivefilm forms the hollow bump structure having an open mouth above thephotoresist layer; removing the photoresist layer so that the open mouthof the hollow bump structure extends above the molding plate; joiningthe open mouth of the hollow bump structure to a substrate; and removingthe molding plate to leave the hollow bump structure on the substrate.10. The method of claim 9, wherein the step of forming the photoresistlayer includes forming the photoresist layer on an interior part of theconcave mold so that an exterior of the hollow bump structure isindented at the interior part.
 11. The method of claim 9, wherein theopen mouth of the hollow bump structure extends radially beyond aperiphery of the concave mold after the photoresist layer is removed.12. The method of claim 9, wherein the step of depositing the conductivefilm comprises the steps of depositing at least two different materialswith different electrical characteristics.